The present invention relates to a semiconductor device, and more particularly, to a method for fabricating a photomask which can correct an error in a critical dimension (CD) of a fine pattern.
In a fabricating process of semiconductor devices, a photolithography process is performed several times to form components on a semiconductor substrate. A photomask with a fine pattern is needed for forming a highly integrated circuit through the photolithography process. In addition, the high integration of semiconductor devices requires a high uniformity in a critical dimension (CD) of a pattern.
A binary mask is generally used as a photomask. The binary mask is fabricated by forming a light blocking layer on a transparent substrate and etching the light blocking layer into a predetermined pattern such that transmitted light penetrates only the substrate and is irradiated on a wafer. However, in order to form a finer pattern, a half-tone phase shift mask has been proposed which can form a finer pattern (as compared with a binary mask) on a wafer by using a phase shift material with transmittance of a few percent.
FIGS. 1A to 1C illustrate cross-sectional views of a conventional photomask.
Referring to FIG. 1A, a phase shift layer 102 and a light blocking layer 104 are sequentially deposited on a transparent substrate 100. A photoresist pattern 106 exposing a portion of the light blocking layer 104 is formed by depositing and patterning a photoresist layer.
Referring to FIG. 1B, a light blocking pattern 108 and a phase shift pattern 110, which define a phase shift region 112 and a light transmitting region 114, are formed by etching the exposed light blocking layer 104 and phase shift layer 102 using the photoresist pattern 106 as a mask so as to selectively expose the transparent substrate 100. The photoresist pattern 106 and the light blocking pattern 108 are removed. Consequently, a phase shift mask pattern 116 including the phase shift region 112 and the light transmitting region 114 is formed on the transparent substrate 100, as illustrated in FIG. 1C.
The phase shift mask pattern 116A is formed by etching a thin layer using the photoresist pattern 106 as an etch mask. In this case, the phase shift mask pattern 116 formed on the transparent substrate 100 may not satisfy a desired condition.
More specifically, referring to FIG. 1C, when the phase shift mask pattern 116 is formed by etching a thin layer using the photoresist pattern 106 as an etch mask, a CD of the phase shift mask pattern 116 formed on the transparent substrate 100 may become smaller than the desired condition, which is indicated by a reference symbol “a”, or become larger than the desired condition, which is indicated by a reference symbol “b”. When a pattern formed by etching a thin layer cannot satisfy the desired condition, it is difficult to control the CD after the etching process. Therefore, the fabricated photomask may be discarded and a new photomask would need to be fabricated.